The present invention relates to a sintered silicon carbide composite and, more in particular, relates to a sintered silicon carbide composite which shows low specific electrical resistivity and excellent electroconductivity, has easy fabricability for electric discharge machining and excellent mechanical strength, and can be used as structural material.
Silicon carbide is a covalent bond compound having high hardness and rigidity, low heat expansion coefficient and high decomposing temperature, and high density sintered products obtained therefrom are useful as light-weight temperature-resistant material having great strength at high temperature, high heat impact resistance and excellent abrasion resistance.
Among them, those of excellent electric insulating property and heat conductivity are used for IC substrates, electronic materials, etc.
As sintered silicon carbide product of this type, those prepared by adding carbide, nitride or boride of elements belonging to the groups IIIa or IVa of the periodical table to powdery silicon carbide and then subjecting to hot-press sintering treatment have been proposed.
For example, there have been proposed in, for example,
Japanese Patent Publication No. 63-13955 (corresponding to U.S. patent application Ser. No. 161,726 filed on June 23, 1980); "a process for producing mixed ceramic articles, comprising: PA0 Japanese Patent Application Laid-Open (KOKAI) No. 61-26565; "a process for producing sintered SiC products, comprising: PA0 Japanese Patent Application Laid-Open (KOKAI) No. 61-26566; "a method of a sintered SiC composite, comprising: PA0 Japanese Patent Application Laid-Open (KOKAI) No. 62-3072; "sintered silicon carbide products comprising:
(a) mixing about from 5 to 95 parts by weight of silicon carbide of less than 1 .mu.m, about from 5 to 95 parts by weight of fine titanium diboride, about from 0.5 to 5.0 parts by weight of carbon or carbon source material and about from 0.2 to 3.0 parts by weight of a sintering aid, PA1 (b) forming the mixture into a product having a shape of an aimed article and, PA1 (c) sintering the thus formed product in a solid phase under substantially normal pressure, thereby obtaining a sintered article containing silicon carbide and titanium diboride", PA1 molding a mixture comprising at least one additive of Be, B, Al, an element of group IVa, an element of group Va, an element of group VIa or an ingredient containing such elements and the balance substantially composed of SiC, and sintering the thus molded mixture in a non-oxidative atmosphere, wherein Al or Al-containing ingredient is present together to the outside of the molding product": PA1 molding a mixture comprising from 0.01 to 20% by weight (calculated as Al) of Al-containing ingredient as sintering aid, not less than 0.1% by weight of at least one of Be, B, Al, an element of group IVa, an element of group Va or an element of group VIa as an additive and the balance substantially comprised of SiC, and then sintering the thus molded mixture in a non-oxidative atmosphere": and PA1 silicon carbide, from 0.5 to 35% by weight (calculated as Al to silicon carbide) of Al and/or refractory Al compound and from 2 to 99% by weight of boride of elements belonging to the group IVa, Va or VIa in the 4th, 5th and sixth period of the periodical table based on silicon carbide, as the main ingredient, and having such a structure that more than one-half amount of crystalline silicon carbide particles comprise columnar and/or plate-like crystalline silicon carbide particles", respectively.
However, if carbide, nitride or boride of elements belonging to the group IIIa or IVa of the periodical table is blended by a considerable amount in order to lower the specific electrical resistivity to ensure electroconductivity, (i) blending amount of silicon carbide is reduced relatively tending to worsen the sintering property, whereby (ii) it is necessary to produce sintered product by hot-press sintering process, and (iii) this makes it impossible to form a complicated shape for the sintered product and, as a result, (iv) the utilizable range as the structural material may be remarkably restricted sometimes.
For overcoming these problems, as a result of the present inventors' earnest study, it has been found out that a sintered silicon carbide composite obtained by sintering a blend comprising from 25 to 85% by weight of powdery silicon carbide, from 1 to 25% by weight of at least one of chromium and chromium compound, from 10 to 70% by weight of at least one of carbide, nitride and boride of elements belonging to the elements IVb and Vb of the periodical table, and 3 to 25% by weight of aluminum oxide, in an inert gas atmosphere at a temperature from 1700.degree. to 1100.degree. C. has low specific electrical resistivity, high electroconductivity and, excellent in mechanical strength, it is easy for electric discharge machining and can be utilizable also as structural materials. Based on this finding, the present invention has been attained.